1. Field of the Invention
This invention relates to magnetic disk drives that read and write data on magnetic disks in response to commands given from host systems. Particularly, this invention relates to video recording/reproduction systems that use the magnetic disk drives to perform video recording and reproduction under control of the host systems.
This application is based on Patent Application No. Hei 10-322666 filed in Japan, the content of which is incorporated herein by reference.
2. Description of the Related Art
A variety of papers disclose the technologies regarding the magnetic disk drives and video recording/reproduction systems, as follows:
For example, Japanese Patent Application, First Publication No. Hei 10-49312 discloses a magnetic disk drive, which uses a nonvolatile memory to speed up the processing, regarding recording and reproduction of data on magnetic recording media, by eliminating an access time for an access to an alternative sector address which is physically discontinuous.
Japanese Patent Application, First Publication No. Hei 7-307061 discloses a recording and reproducing device, which is designed to reduce recording time and reproducing time even if a disk contains a defective sector by accessing its alternative sector within a solid memory.
Japanese Patent Application, First Publication No. Hei 8-76933 discloses an example of a format operation controller, in which an alternative sector process and/or defective sector mapping is performed with respect to a defective sector detected on a new hard disk to record picture data.
In the magnetic disk drives, magnetic heads perform magnetization on magnetic layers corresponding to surfaces of magnetic disks, which rotate at high speed. Thus, the magnetic disk drives are capable of recording and reproducing desired data on the magnetic disks. Normally, the magnetic heads fly over the magnetic disks, which rotate at high speed, by some gaps to read and write data without making contact with the disk surfaces. Recently, the gaps by which the magnetic heads fly over the rotating magnetic disks are reduced to cope with increases in capacities and recording densities of the magnetic disk drives. Such reduction of the gaps makes the magnetic heads to easily come in contact with the disk surfaces. When magnetoresistance effect components are used for reproduction heads, disturbances are introduced into reproduction waveforms due to so-called xe2x80x9cthermal asperityxe2x80x9d, which correspond to rapid temperature variations of the components being caused by contacts between the heads and disks. For this reason, it is required to reduce roughness of the disk surfaces and disturbance (or partial defectiveness) of the magnetic layers more strictly.
However, it is almost impossible to perfectly eliminate defects of the disks in manufacture. So, manufacturers make the magnetic disk drives in consideration of the defects of the disks to some extent. In order to use the disks having such defects without troubles, the magnetic disk drives are generally designed to effect defect repair processes, which are called xe2x80x9creassignment processes (or alternate processes)xe2x80x9d, when detecting defects of the disks. According to the reassignment process, the magnetic disk drive recognizes an area (i.e., sector), on which a recording/reproduction process cannot be performed normally due to existence of a defect, as a defect sector. Specifically, the magnetic disk drive stops using such a defect sector by recording data representative of existence of the defect in a header portion (i.e., ID portion) of the defect sector. Herein, an alternate sector region is prepared in advance for replacement of the defect sector on a same track of the defect sector or within a zone containing the defect sector. From such an alternate sector region, the magnetic disk drive determines and assigns an alternate destination sector. In addition, the magnetic disk drive stores information representative of a location of the defect sector to the magnetic disk or a prescribed memory provided inside thereof. Thus, the magnetic disk drive controls such that access to the defect sector is changed over to access to the alternate destination sector of the alternate sector region.
Enlargement of capacities of the magnetic disk drives is achieved mainly by reduction of record bit lengths as well as by increase of record track densities. High track densities inevitably require servo control techniques for accurate positioning of heads on desired track positions. Particularly, in order to cope with environmental variations in temperature and humidity as well as mechanical variations when the magnetic disk drives operate for a long time, it is necessary to perform calibration of servo control system every prescribed time with respect to the magnetic disks of high track densities. There are provided a variety of examples for the calibration, as follows:
i) Circuit/HDA calibration for performing corrections specifically with respect to circuit boards and head disk assembly (HDA);
ii) Calibration (head sensitivity correction) for accuracy of positional error signals;
iii) Disk eccentric calibration;
iv) Calibration (current/acceleration reduced gain) for voice coil motor (VCM) control system that drives a head arm to move to a predetermined position; and
v) Calibration for external forces such as wind pressure being applied to the head arm or flexible printed-circuit board (FPC).
The aforementioned reassignment process and calibration process are performed in factory shipment inspection, which is made just before shipment of products corresponding to the magnetic disk drives, or when the users start to operate the magnetic disk drives. As for the circuit/HDA calibration, data are measured in the factory shipment inspection and are recorded on a memory such as a ROM provided in the magnetic disk drive. Such data can be used for corrections of the magnetic disk drive after the shipment. In contrast, the reassignment process is effected with respect to the defect sector which occurs after the shipment, while time-related variations (e.g., temperature variations) may be included in the disk eccentric calibration and VCM control system calibration after the shipment. So, they must be performed after the shipment or when the user starts to operate the magnetic disk drive.
Video recording/reproduction systems conventionally use the aforementioned magnetic disk drives for recording and reproduction of video information on the magnetic disks. However, the conventional video recording/reproduction system using the magnetic disk drive suffers from a variety of problems as follows:
i) A first problem is that the system badly records and reproduces video images which may be interrupted intermittently due to the reassignment process and calibration, so the magnetic disk drive is damaged in reliability while picture quality of display is damaged. Because, when the reassignment process is performed due to occurrence of the defect sector in the magnetic disk storing the video data having continuity or when the calibration is performed at certain intervals of time while the magnetic disk drive is operating to read or write video data having continuity, such continuity of the video data must be interrupted (intermittently).
ii) A second problem is that when the user starts video recording at an arbitrary time, the video recording cannot be started instantaneously, so some part of vido images must be broken without being recorded on the disk. Because, in some cases, the magnetic disk drive performs the calibration at the timing when the host machine issues a record start instruction. At that time, the magnetic disk drive is occupied in calibration, so the system cannot execute the record start instruction immediately.
It is an object of the invention to provide a video recording/reproduction system using a magnetic disk drive, which is improved in reliability by controlling a reassignment process and calibration in such a way that recording and reproducing operations are adequately performed with respect to video data having continuity to suppress occurrence of breaks in video images.
A video recording/reproduction system of this invention is equipped with a magnetic disk drive, which records and reproduces video data on a magnetic disk by driving a magnetic head. Herein, the magnetic disk drive is controlled by a CPU in accordance with control programs, while a host machine is equipped with an antenna, a tuner, a monitor and a timer to perform a variety of controls regarding recording and reproduction with respect to the magnetic disk drive in accordance with commands being given from an operation panel which is manipulated by a human operator.
At a recording mode, the host machine controls the magnetic disk drive to record a broadcast program, being selected by the tuner, on the magnetic disk. At a reproduction mode, the host machine controls the magnetic disk drive to reproduce data from the magnetic disk so that the monitor displays pictures corresponding to the reproduced data on a screen.
In an access failure state where the CPU fails to access a target sector of the magnetic disk so that the target sector is regarded as a defect sector, the magnetic disk drive performs a reassignment process, in which an alternate sector is assigned as alternate destination for the defect sector to perform recording or reproduction. Herein, a decision whether to perform the reassignment process is made based on a maximum transfer speed of the magnetic disk drive, a data transfer speed by which data are transferred between the host machine and magnetic disk drive, and vacant capacity of a buffer memory built in the magnetic disk drive. Specifically, the vacant capacity is divided by a difference between the maximum transfer speed and data transfer speed to produce a first time, which is compared with a second time required for execution of the reassignment process. If the first time is greater than the second time, the CPU determines to perform the reassignment process. If the first time is under the second time so that data being transferred from the host machine may overflow the buffer memory by execution of the reassignment process, the CPU temporarily refuges the data to a storage, then, after completion of recording or reproduction, the CPU performs the reassignment process so that the data are recorded or reproduced on the alternate sector of the magnetic disk. Incidentally, the CPU determines the alternate sector with reference to an alternate sector using condition table for storing a plurality of alternate sectors which are selected in advance and each of which is assigned as alternate destination for the defect sector, while the CPU makes a decision whether to access the alternate sector because the target sector corresponds to the defect sector with reference to an alternate destination assignment condition table for storing relationship between position information of the defect sector and position information of the alternate sector being assigned.
Further, the magnetic disk drive performs calibration with respect to the magnetic disk only when a time margin between a present time measured by the timer and a start time of reserved recording in which the host machine stores a reservation time for recording of a broadcast program is greater than a calibration time required for execution of the calibration.
Thus, it is possible to suppress reduction of the transfer speed, in other words, reduction of throughput of video data due to execution of the reassignment process and calibration. In addition, it is possible to avoid occurrence of breaks by which pictures being recorded or reproduced are interrupted intermittently. So, it is possible to improve reliability in performance and operation of the magnetic disk drive as well as picture quality in recording and reproduction.